From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-16.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1406DC433F5 for ; Wed, 8 Sep 2021 00:43:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EA73F61130 for ; Wed, 8 Sep 2021 00:43:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S245041AbhIHAoZ (ORCPT ); Tue, 7 Sep 2021 20:44:25 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:26331 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229946AbhIHAoW (ORCPT ); Tue, 7 Sep 2021 20:44:22 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1631061795; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=dmVzBjVacbNmPCi8K+Po+kbIXEQdRx5SLN91yaB+v4A=; b=VRuODBURNNxAs0jfb3xLd1VVQpScjro2igtSoDlbUB2JKNCL+HJXH9vLfwVyhIvMujXidq ivx/EhEuqmSPwSfJT4JX73Cm8/vfhQI391Pd6buMhux5/fVj0oZrSF2OIekxxnCJGXTA5c fDd2eCMO40ZSLXh7PLbfzmmiI2RnQhM= Received: from mail-qk1-f200.google.com (mail-qk1-f200.google.com [209.85.222.200]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-436-S5nPZgJjNlioV1oSV_8TUw-1; Tue, 07 Sep 2021 20:43:14 -0400 X-MC-Unique: S5nPZgJjNlioV1oSV_8TUw-1 Received: by mail-qk1-f200.google.com with SMTP id 70-20020a370b49000000b003d2f5f0dcc6so944710qkl.9 for ; Tue, 07 Sep 2021 17:43:14 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=dmVzBjVacbNmPCi8K+Po+kbIXEQdRx5SLN91yaB+v4A=; b=gEWMEYJm4b6U/l51SjSGo3AikotKku7jQtwcpf4DMBrsKOEsNmlLiL3LN0mKBQ53dy K9A9fJ8wdYTl9NrSMTwZ5iEWhvtgDT2mUFEefiGdsDbJdejNosDO9AsgKYQcXhN5Mxmf H+hAaXBe2f91Vo9ApnCR4L8P8Ccw9uJsd8LHOHD7Ed8gUpGkWqHB4gFjQxBmjUuyrr12 97B/xuPG2zwycWyJitMeWuyv2rCsRkwhZIL2jjwtYkxi9oQRjYU/WJtXlQYOWd+phsB4 yoGTFwrAlKuND4/mat81Y+hIRhQ17+pjoXc3pqwSxrKXgwNlSYnvjrEDf+0h9lQlKeTK Otzw== X-Gm-Message-State: AOAM533vx+SsrdehAR1S1Qhy0VRa+bYGi9nfL6ykheVXG9dpudnpeXAU rzEM+aE6aiAAQoUSkL9NgSPvkWN/IkmRiaT50OEAXjKZ0ga0CZb/f0W6yi5uGSYx2XTScfOYROW Xtna4ngXGTIk6jzxcKj+PleA9 X-Received: by 2002:a37:6d7:: with SMTP id 206mr1026333qkg.251.1631061793575; Tue, 07 Sep 2021 17:43:13 -0700 (PDT) X-Google-Smtp-Source: ABdhPJwzQ3LdxwdgLnAJnpBB6RNLoLM2zvGQzMql6sXI/lPCNdVVaY2yyz9rmAH7cQWSUQWuOeDfZw== X-Received: by 2002:a37:6d7:: with SMTP id 206mr1026314qkg.251.1631061793298; Tue, 07 Sep 2021 17:43:13 -0700 (PDT) Received: from t490s ([2607:fea8:56a3:500::ad7f]) by smtp.gmail.com with ESMTPSA id 207sm539602qkh.45.2021.09.07.17.43.11 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 07 Sep 2021 17:43:12 -0700 (PDT) Date: Tue, 7 Sep 2021 20:43:11 -0400 From: Peter Xu To: David Hildenbrand Cc: linux-mm@kvack.org, Hugh Dickins , Andrew Morton , linux-kernel@vger.kernel.org, Miaohe Lin , Matthew Wilcox , Yang Shi , "Kirill A . Shutemov" , Jerome Glisse , Alistair Popple , Andrea Arcangeli , Mike Rapoport Subject: Re: [PATCH v2 5/5] mm: Add ZAP_FLAG_SKIP_SWAP and zap_flags Message-ID: References: <20210902201721.52796-1-peterx@redhat.com> <20210902201836.53605-1-peterx@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Sep 03, 2021 at 09:25:51AM +0200, David Hildenbrand wrote: > On 02.09.21 22:18, Peter Xu wrote: > > Firstly, the comment in zap_pte_range() is misleading because it checks against > > details rather than check_mappings, so it's against what the code did. > > > > Meanwhile, it's confusing too on not explaining why passing in the details > > s/on// > > > pointer would mean to skip all swap entries. New user of zap_details could > > very possibly miss this fact if they don't read deep until zap_pte_range() > > because there's no comment at zap_details talking about it at all, so swap > > entries could be errornously skipped without being noticed. > > s/errornously/erroneously/ Will fix, thanks. > > > > > Actually very recently we introduced unmap_mapping_page() in 22061a1ffabd, I > > think that should also look into swap entries. Add a comment there. IOW, this > > patch will be a functional change to unmap_mapping_page() but hopefully in the > > right way to do it. I'll remove this paragraph, as explained elsewhere. > > > > This partly reverts 3e8715fdc03e ("mm: drop zap_details::check_swap_entries"), > > but introduce ZAP_FLAG_SKIP_SWAP flag, which means the opposite of previous > > "details" parameter: the caller should explicitly set this to skip swap > > entries, otherwise swap entries will always be considered (which should still > > be the major case here). > > > > Cc: Kirill A. Shutemov > > Cc: Hugh Dickins > > Signed-off-by: Peter Xu > > --- > > include/linux/mm.h | 16 ++++++++++++++++ > > mm/memory.c | 6 +++--- > > 2 files changed, 19 insertions(+), 3 deletions(-) > > > > diff --git a/include/linux/mm.h b/include/linux/mm.h > > index 81e402a5fbc9..a7bcdb2ec956 100644 > > --- a/include/linux/mm.h > > +++ b/include/linux/mm.h > > @@ -1716,12 +1716,18 @@ static inline bool can_do_mlock(void) { return false; } > > extern int user_shm_lock(size_t, struct ucounts *); > > extern void user_shm_unlock(size_t, struct ucounts *); > > +typedef unsigned int __bitwise zap_flags_t; > > + > > +/* Whether to skip zapping swap entries */ > > +#define ZAP_FLAG_SKIP_SWAP ((__force zap_flags_t) BIT(0)) > > Interestingly, this will also skip fake some swap entries (e.g., migration > entries but not private/exclusive entries). Maybe extend that documentation > a bit. > > ... but, looking into zap_pmd_range(), we don't care about "details" when > calling zap_huge_pmd(), which will zap pmd migration entries IIUC ... so > it's really unclear to me what the flag (and current behavior) really is and > what should be documented. Should we maybe really only care about "real" > swap entries? Indeed, I tried to look into it today and see why we wanted to skip swap entries but I failed to figure it out easily - it goes back to the 1st git commit of Linux. Maybe there'll be some experienced developer who knows the history, but before that I decided to just keep the behavior. The final goal of mine is to make the code clean and also prepares for the uffd-wp that will allow free-style use of "details" pointer, rather than have an implicit hint on "skip swap entry" then it'll be enough for this patch. > > Most probably I'm just missing something important. > > > + > > /* > > * Parameter block passed down to zap_pte_range in exceptional cases. > > */ > > struct zap_details { > > struct address_space *zap_mapping; /* Check page->mapping if set */ > > struct page *single_page; /* Locked page to be unmapped */ > > + zap_flags_t zap_flags; /* Extra flags for zapping */ > > }; > > /* > > @@ -1737,6 +1743,16 @@ zap_skip_check_mapping(struct zap_details *details, struct page *page) > > return details->zap_mapping != page_rmapping(page); > > } > > +/* Return true if skip swap entries, false otherwise */ > > +static inline bool > > +zap_skip_swap(struct zap_details *details) > > +{ > > + if (!details) > > + return false; > > + > > + return details->zap_flags & ZAP_FLAG_SKIP_SWAP; > > +} > > + > > struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr, > > pte_t pte); > > struct page *vm_normal_page_pmd(struct vm_area_struct *vma, unsigned long addr, > > diff --git a/mm/memory.c b/mm/memory.c > > index e5ee8399d270..4cb269ca8249 100644 > > --- a/mm/memory.c > > +++ b/mm/memory.c > > @@ -1379,8 +1379,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb, > > continue; > > } > > - /* If details->check_mapping, we leave swap entries. */ > > - if (unlikely(details)) > > + if (unlikely(zap_skip_swap(details))) > > continue; > > if (!non_swap_entry(entry)) > > @@ -3351,6 +3350,7 @@ void unmap_mapping_page(struct page *page) > > first_index = page->index; > > last_index = page->index + thp_nr_pages(page) - 1; > > + /* Keep ZAP_FLAG_SKIP_SWAP cleared because we're truncating */ As to keep the behavior, I shouldn't fiddle around with this, so I'll also attach ZAP_FLAG_SKIP_SWAP to unmap_mapping_page() too in v3. > > details.zap_mapping = mapping; > > details.single_page = page; Thanks, -- Peter Xu